A wide variety of roller cone drill bits have previously been used to form wellbores in downhole formations. Such drill bits may also be referred to as “rotary” cone drill bits. Roller cone drill bits frequently include a bit body with three support arms extending therefrom. A respective cone is generally rotatably mounted on each support arm opposite from the bit body. Such drill bits may also be referred to as “tricone drill bits” or “rock bits”.
A wide variety of roller cone drill bits have been satisfactorily used to form wellbores. Examples include roller cone drill bits with only one support arm and one cone, two support arms with a respective cone rotatably mounted on each arm and four or more cones rotatably mounted on an associated bit body. Various types of cutting elements and cutting structures such as compacts, inserts, milled teeth and welded compacts have also been used in association with roller cone drill bits.
Cutting elements and cutting structures associated with roller cone drill bits typically form a wellbore in a subterranean formation by a combination of shearing and crushing adjacent portions of the formation. The shearing motion may also be described as each cutting element scraping portions of the formation during rotation of an associated cone. The crushing motion may also be described as each cutting element penetrating portions of the formation during rotation of an associated cone. Within the well drilling industry it is generally accepted that shearing or scraping motion of a cutting element is a more efficient technique for removing a given volume of formation material from a wellbore as compared with a cutting element crushing or penetrating the same formation. Fixed cutter drill bits, sometimes referred to as drag bits or PDC drill bits, typically have cutting elements or cutting structures which only shear or scrape during contact with a formation. Therefore, fixed cutter drill bits are often used to form a wellbore in soft and medium formations. Conventional roller cone drill bits often require more time to drill soft and medium formations as compared to fixed cutter drill bits.
The magnitude of the shearing motion or scraping motion associated with cutting structures of roller cone drill bits depends upon various factors such as the offset of each cone and associated cone profile. The magnitude of the crushing motion or penetrating motion associated with cutting structures of roller cone drill bits depends upon various factors such as weight on the bit, speed of rotation and geometric configuration of associated cutting structures and associated cone profiles. Roller cone drill bits designed for drilling relatively soft formations often have a larger cone offset value as compared with roller cone drill bits designed for drilling hard formations. Roller cone drill bits having cutting structures formed by milling rows of teeth on each cone are often used for drilling soft formations. Roller cone drill bits having cutting elements and cutting structures formed from a plurality of hard metal inserts or compacts are often used for drilling medium and hard formations. It is well known in the roller cone drill bit industry that drilling performance may be improved by orientation of cutting elements and cutting structures disposed on associated cones. Roller cone drill bits often remove a greater volume of formation material by shearing or scraping as compared with crushing or penetrating of the same formation.